Adding a KHR_animation2 extension

extensions/2.0/Khronos/KHR_animation_pointer/README.md

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+# KHR\_animation_pointer
+
+## Contributors
+
+* Alexey Knyazev
+* Ben Houston, Threekit
+* Bryce Hutchings, Microsoft [@brycehutchings](https://twitter.com/brycehutchings)
+* Don McCurdy
+* Ed Mackey, AGI @emacke
+* Felix Herbst, prefrontal cortex [@hybridherbst](https://twitter.com/hybridherbst)
+* Gary Hsu, Microsoft [@bghgary](https://twitter.com/bghgary)
+* Jamie Marconi, Microsoft [@najadojo](https://twitter.com/najadojo)
+* Joe Herdman, [@jbherdman](https://github.com/jbherdman)
+* Lewis Weaver, Microsoft
+* Marco Hutter
+* Norbert Nopper, UX3D [@UX3DGpuSoftware](https://twitter.com/UX3DGpuSoftware)
+
+Copyright (C) 2018-2022 The Khronos Group Inc. All Rights Reserved. glTF is a trademark of The Khronos Group Inc.
+See [Appendix](#appendix-full-khronos-copyright-statement) for full Khronos Copyright Statement.
+
+## Status
+
+Draft
+
+## Dependencies
+
+Written against the glTF 2.0 spec.
+
+## Overview
+
+This extension is based on the animation features of glTF 2.0. The structure of the schemas stay the same.  
+
+The only major addition is, that the output values are mapped using a [JSON Pointer](https://datatracker.ietf.org/doc/html/rfc6901).
+
+### Motivation
+
+At this point of time, one can only target the transformation or weight data of a node.  
+With this extension, one can technically target any value (`scalar`, `vec2`, `vec3`, `vec4` and scalars in an `array`) in glTF e.g.
+
+* Color factors in materials
+* Camera field of view
+
+Even using a JSON pointer, the targets and their expected behavior are explictly defined.
+
+Current and future extensions have to write against this specification to allow to animate specific values.
+
+#### Current and future restrictions
+
+The calculated values can be out of range of the minimum and maximum value, however the values have to be clamped using the properties min and max value before setting the value.
+
+##### Not animatable properties
+
+`glTFid`
+
+It is not allowed to animate a glTFid property, as it does change the structure of the glTF in general.
+
+### Valid target templates
+
+|`path`                                                |Accessor Type|Component Type(s)  |Description                                                   |
+|------------------------------------------------------|-------------|-------------------|--------------------------------------------------------------|
+|`"/nodes/{}/matrix"`                                  |`"SCALAR"`   |`5126` (FLOAT)|Matrix elements                                               |
+|`"/nodes/{}/rotation"`                                |`"VEC4"`     |`5126`&nbsp;(FLOAT)<br>`5120`&nbsp;(BYTE)&nbsp;normalized<br>`5121`&nbsp;(UNSIGNED_BYTE)&nbsp;normalized<br>`5122`&nbsp;(SHORT)&nbsp;normalized<br>`5123`&nbsp;(UNSIGNED_SHORT)&nbsp;normalized|XYZW rotation quaternion|
+|`"/nodes/{}/scale"`                                   |`"VEC3"`     |`5126`&nbsp;(FLOAT)|XYZ scale vector                                              |
+|`"/nodes/{}/translation"`                             |`"VEC3"`     |`5126`&nbsp;(FLOAT)|XYZ translation vector                                        |
+|`"/nodes/{}/weights"`                                 |`"SCALAR"`   |`5126`&nbsp;(FLOAT)<br>`5120`&nbsp;(BYTE)&nbsp;normalized<br>`5121`&nbsp;(UNSIGNED_BYTE)&nbsp;normalized<br>`5122`&nbsp;(SHORT)&nbsp;normalized<br>`5123`&nbsp;(UNSIGNED_SHORT)&nbsp;normalized|Morph target weights                                          |
+|`"/cameras/{}/orthographic/xmag"`                     |`"SCALAR"`   |`5126`&nbsp;(FLOAT)|Horizontal magnification of the view                          |
+|`"/cameras/{}/orthographic/ymag"`                     |`"SCALAR"`   |`5126`&nbsp;(FLOAT)|Vertical magnification of the view                            |
+|`"/cameras/{}/orthographic/zfar"`                     |`"SCALAR"`   |`5126`&nbsp;(FLOAT)|Distance to the far clipping plane                            |
+|`"/cameras/{}/orthographic/znear"`                    |`"SCALAR"`   |`5126`&nbsp;(FLOAT)|Distance to the near clipping plane                           |
+|`"/cameras/{}/perspective/aspectRatio"`               |`"SCALAR"`   |`5126`&nbsp;(FLOAT)|Aspect ratio of the field of view                             |
+|`"/cameras/{}/perspective/yfov"`                      |`"SCALAR"`   |`5126`&nbsp;(FLOAT)|Vertical field of view in radians                             |
+|`"/cameras/{}/perspective/zfar"`                      |`"SCALAR"`   |`5126`&nbsp;(FLOAT)|Distance to the far clipping plane                            |
+|`"/cameras/{}/perspective/znear"`                     |`"SCALAR"`   |`5126`&nbsp;(FLOAT)|Distance to the near clipping plane                           |
+|`"/materials/{}/pbrMetallicRoughness/baseColorFactor"`|`"VEC4"`     |`5126`&nbsp;(FLOAT)<br>`5120`&nbsp;(BYTE)&nbsp;normalized<br>`5121`&nbsp;(UNSIGNED_BYTE)&nbsp;normalized<br>`5122`&nbsp;(SHORT)&nbsp;normalized<br>`5123`&nbsp;(UNSIGNED_SHORT)&nbsp;normalized|The material's base color factor|
+|`"/materials/{}/pbrMetallicRoughness/metallicFactor"` |`"SCALAR"`   |`5126`&nbsp;(FLOAT)|The metalness of the material                                 |
+|`"/materials/{}/pbrMetallicRoughness/roughnessFactor"`|`"SCALAR"`   |`5126`&nbsp;(FLOAT)|The roughness of the material                                 |
+|`"/materials/{}/alphaCutoff"`                         |`"SCALAR"`   |`5126`&nbsp;(FLOAT)|The alpha cutoff value of the material                        |
+|`"/materials/{}/emissiveFactor"`                      |`"VEC3"`     |`5126`&nbsp;(FLOAT)|The emissive color of the material                            |
+|`"/materials/{}/normalTexture/scale"`                 |`"SCALAR"`   |`5126`&nbsp;(FLOAT)|Multiplier applied to each normal vector of the normal texture|
+|`"/materials/{}/occlusionTexture/strength"`           |`"SCALAR"`   |`5126`&nbsp;(FLOAT)|Multiplier controlling the amount of occlusion applied        |
+
+##### `extras`
+
+A channel may target `extras` at any allowed JSON Pointer value but
+interpretation of the animated values is entirely application specific.
+
+## Extension compatibility and fallback behavior
+
+If this extension is used, the `animation.channel.target.node` **must not** be set.
+Because the node isn’t defined, the channel is ignored and not animated due to the current specification.  
+If this extension is used, the `animation.channel.target.path` **must** contain the new `pointer` constant value.
+
+### Animating properties of extensions
+
+Extensions created after KHR_animation_pointer should state which properties can be animated and which cannot.  
+The following extensions have been created before KHR_animation_pointer and are thus listed here with their animatable properties:  
+
+#### [KHR_draco_mesh_compression](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_draco_mesh_compression)
+❌ No animatable properties.
+
+#### [KHR_lights_punctual](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_lights_punctual)
+| Property | Animatable |
+|:-----|:------|
+| `name` | ❌ |
+| `color` | ✅ |
+| `intensity` | ✅ |
+| `type` | ❌ |
+| `range` | ✅ |
+| `spot.innerConeAngle` | ✅ |
+| `spot.outerConeAngle` | ✅ |
+
+#### [KHR_materials_clearcoat](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_clearcoat)
+| Property | Animatable |
+|:----|:-------|
+| `clearcoatFactor` | ✅ |
+| `clearcoatTexture` | ❌ |
+| `clearcoatRoughnessFactor` | ✅ |
+| `clearcoatRoughnessTexture` | ❌ |
+| `clearcoatNormalTexture` | ❌ |
+
+#### [KHR_materials_ior](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_ior)
+| Property | Animatable |
+|:-----|:------------|
+| `ior` | ✅ |
+
+#### [KHR_materials_sheen](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_sheen)
+| Property | Animatable |
+|:-----|:------------|
+| `sheenColorFactor` | ✅ |
+| `sheenColorTexture` | ❌ |
+| `sheenRoughnessFactor` | ✅ |
+| `sheenRoughnessTexture` | ❌ |
+
+#### [KHR_materials_specular](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_specular)
+| Property | Animatable |
+|:--------|:----------|
+| `specularFactor` | ✅ |
+| `specularTexture` | ❌ |
+| `specularColorFactor` | ✅ |
+| `specularColorTexture` | ❌ |
+
+#### [KHR_materials_transmission](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_transmission)
+| Property | Animatable |
+|:--------|:----------|
+| `transmissionFactor` | ✅ |
+| `transmissionTexture` | ❌ |
+
+#### [KHR_materials_unlit](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_unlit)
+❌ No animatable properties.
+
+#### [KHR_materials_variants](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_variants)
+❌ No animatable properties.
+
+#### [KHR_materials_volume](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_volume)
+| Property | Animatable |
+|:--------|:----------|
+| `thicknessFactor` | ✅ |
+| `thicknessTexture` | ❌ |
+| `attenuationDistance` | ✅ |
+| `attenuationColor` | ✅ |
+
+#### [KHR_mesh_quantization](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_mesh_quantization)
+❌ No animatable properties.
+
+#### [KHR_texture_basisu](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_texture_basisu)
+❌ No animatable properties.
+
+#### [KHR_texture_transform](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_texture_transform)
+| Property | Animatable |
+|:--------|:----------|
+| `offset` | ✅ |
+| `rotation` | ✅ |
+| `scale` | ✅ |
+| `texCoord` | ❌ |
+
+#### [KHR_xmp_json_ld](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_xmp_json_ld)
+❌ No animatable properties.
+
+### Example target templates for extensions
+
+|`path`                                                |Accessor Type|Component Type(s)  |Description                                                   |
+|------------------------------------------------------|-------------|-------------------|--------------------------------------------------------------|
+|`"/materials/{}/pbrMetallicRoughness/baseColorTexture/extensions/KHR_texture_transform/offset"`                                  |`"SCALAR"`   |`5126`&nbsp;(FLOAT)|XY offset vector                                               |
+
+## glTF Schema Updates
+
+* **JSON schema**: [glTF.KHR_animation_pointer.schema.json](schema/glTF.KHR_animation_pointer.schema.json)
+
+## Notes and clarifications
+
+### JSON Pointer
+
+For a `scalar` value, the JSON Pointer targets the glTF property.  
+This means, the property is replaced by the interpolated value.
+
+For any other case, the JSON Pointer targets the glTF property as well but must be an `array` property.  
+This means, that the two or more elements do replace the values in the array.  
+
+## Examples
+
+The following snippet shows the changes for [`animations`](https://github.com/KhronosGroup/glTF-Sample-Models/blob/master/2.0/AnimatedCube/glTF/AnimatedCube.gltf#L117) from the [AnimatedCube](https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0/AnimatedCube) asset.
+
+```javascript
+"animations" : [
+    {
+        "channels" : [
+            {
+                "name" : "Targeting x, y, z, w for a rotation of node at index 0."
+                "sampler" : 0,
+                "target" : {
+                    "path" : "pointer"
+                    "extensions": {
+                        "KHR_animation_pointer" : {
+                            "pointer" : "/nodes/0/rotation"
+                        }
+                    }
+               }
+            }
+        ],
+        "samplers" : [
+            {
+                "input" : 0,
+                "interpolation" : "LINEAR",
+                "output" : 1
+            }
+        ]
+    }
+]
+```
+
+## Appendix: Full Khronos Copyright Statement
+
+Copyright 2018-2022 The Khronos Group Inc.
+
+Some parts of this Specification are purely informative and do not define requirements
+necessary for compliance and so are outside the Scope of this Specification. These
+parts of the Specification are marked as being non-normative, or identified as
+**Implementation Notes**.
+
+Where this Specification includes normative references to external documents, only the
+specifically identified sections and functionality of those external documents are in
+Scope. Requirements defined by external documents not created by Khronos may contain
+contributions from non-members of Khronos not covered by the Khronos Intellectual
+Property Rights Policy.
+
+This specification is protected by copyright laws and contains material proprietary
+to Khronos. Except as described by these terms, it or any components
+may not be reproduced, republished, distributed, transmitted, displayed, broadcast
+or otherwise exploited in any manner without the express prior written permission
+of Khronos.
+
+This specification has been created under the Khronos Intellectual Property Rights
+Policy, which is Attachment A of the Khronos Group Membership Agreement available at
+www.khronos.org/files/member_agreement.pdf. Khronos grants a conditional
+copyright license to use and reproduce the unmodified specification for any purpose,
+without fee or royalty, EXCEPT no licenses to any patent, trademark or other
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+implement the specification and make use of Khronos trademarks in relation to that
+implementation, and receive reciprocal patent license protection under the Khronos
+IP Policy must become Adopters and confirm the implementation as conformant under
+the process defined by Khronos for this specification;
+see https://www.khronos.org/adopters.
+
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extensions/2.0/Khronos/KHR_animation_pointer/schema/glTF.KHR_animation_pointer.schema.json

@@ -0,0 +1,16 @@
+{
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "title": "KHR_animation_pointer glTF extension",
+    "type": "object",
+    "description": "The descriptor of the animated property.",
+    "allOf": [ { "$ref": "glTFProperty.schema.json" } ],
+    "properties": {
+      "pointer": {
+        "type": "string",
+        "description": "JSON pointer of the object to target. The value of the path from animation.channel.target **must** be `pointer`."
+      },
+        "extensions": { },
+        "extras": { }
+    },
+    "required": [ "path" ]
+}